AImageDecoder: Recommend only downscaling with setTargetSize

Fixes: 180037959
Test: NA
Change-Id: I19076b4368623806f7a9f6312a780a6d5886e49e
diff --git a/include/android/imagedecoder.h b/include/android/imagedecoder.h
index cac67d4..ee1eee2 100644
--- a/include/android/imagedecoder.h
+++ b/include/android/imagedecoder.h
@@ -367,6 +367,10 @@
  * the first frame (e.g. before calling {@link AImageDecoder_advanceFrame} or
  * after calling {@link AImageDecoder_rewind}).
  *
+ * It is strongly recommended to use setTargetSize only for downscaling, as it
+ * is often more efficient to scale-up when rendering than up-front due to
+ * reduced overall memory.
+ *
  * Available since API level 30.
  *
  * @param width Width of the output (prior to cropping).